Many systems are provided aboard aircrafts, which consist of mobile parts which have to move.
Wing elements (for example an aileron, a flap, an air brake), elements of the landing gear (for example a landing gear strut movable between an extended position and a retracted position, or a plunger of a brake of a wheel which slides relative to brake friction members), elements making it possible to implement variable geometry turbines, elements of a pump or a fuel metering mechanism, elements of the thrust reversers, elements of a propeller pitch driving mechanism (for example on an helicopter or a turboprop engine), etc. belong to such mobile parts.
On modern aircrafts, more and more electromechanical actuators are used to implement such mobile parts. As a matter of fact, the advantages of using electromechanical actuators are numerous: simple electric distribution and driving, flexibility, simplified maintenance operations, etc.
An electromechanical actuator conventionally comprises a mobile actuating member which moves the mobile part, an electric motor intended to drive the mobile actuating member and thus the mobile part, and one or more sensor(s) for the various parameters of the electromechanical actuator.
An airborne electric actuating system wherein such an electromechanical actuator is integrated conventionally implements the following functions: definition of a set-point according to the function to be fulfilled (for instance a speed, position or force set-point), measurement of one or more electromechanical actuator servo-control parameter(s) (for instance speed, position, force), execution of a servo-control loop enabling the electromechanical actuator to reach the set-point, generation of electric current supplying the electric motor, and transformation, by the electric motor, of the electric energy into a mechanical energy which drives the actuating member and thus the mobile part.
The functions of executing the servo-control loop and generating electric supply current are generally implemented in one or more centralized computer(s): this is called a centralized architecture.
In reference with FIG. 1, a known aircraft brake 1 comprises four electromechanical actuators 2 which are grouped in two distinct arrays of two electromechanical actuators 2. The electromechanical actuators 2 of a distinct array are connected to the same centralized computer 3 positioned in the aircraft bay. The electric motor of each electromechanical actuator 2 receives a three-phase electric current supplying the centralized computer 3 which the electromechanical actuator 2 is connected to, and each electromechanical actuator 2 transmits measurements of a servo-control parameter to the centralized computer 3 (for instance, measurements of the angular position of the rotor of the electric motor).
The generation of the three-phase electric current supplying the electromechanical actuator 2 in such a centralized architecture will now be described in greater details while referring to FIG. 2. A <<high level>> external set-point is generated by external set-point generating means 14 and is transmitted to each centralized computer 3 via a digital bus 15 (a transmission symbolized by reference T1 in FIG. 2). In the case of a braking system architecture, such external set-point is representative of a request for braking generated by a pilot of the aircraft. The external set-point is transmitted to processing means 6 of the centralized computer 3. The processing means 6 of the centralized computer 3 then control and drive the electromechanical actuator 2 including one or more servo-control loop(s). The electromechanical actuator 2 transmits the measurements of one or more servo-control parameter(s) obtained from a sensor 7 to the centralized computer 3, with said measurements being the servo-control loop feedback signal. The servo-control loop output signal is transmitted to a power module 8 drive, then to a power module 9 of the centralized computer 3 which generates the three-phase electric current supplying the electric motor 10 of the electromechanical actuator 2. The electric motor 10 then drives the actuating member 11. Implementing the servo-control loop requires parameters stored in a memory 12 of the centralized computer 3. The power module 9 (which comprises an inverter, for instance) of the centralized computer 3 is supplied by a supply unit 13 outside the centralized computer 3.
It should be noted that such centralized architecture has some drawbacks. First, while referring again to FIG. 1, it can be seen that the architecture shown requires using at least nine electric wires per electromechanical actuator 2: three supply wires 16 for the three phases of the electric motor (symbolized by one single line in FIG. 1), four communication wires 17 (symbolized by a single line in FIG. 1) for sending back to the centralized computers 3 the angular position measurements of the rotor of the electric motor 10, and two supply wires 18 (symbolized by a single line in FIG. 1) for supplying an element for locking the electromechanical actuator 2 making it possible to implement a parking brake. Such electric wires 16, 17, 18 are integrated in cable assemblies which run from the bay to the brake 1 and which are cumbersome and heavy. The extensive length of the cable assemblies wherein the supply wires 16 and thus the currents supplying the electric motors 10 run makes it necessary to use common mode current filtering circuits which increase the mass, complexity and cost of the computers 3.